The weekend before last, I guess. Last weekend, I crashed around three, I was dead tired.
I often stay up until sunrise in the summer half of the year -- the occasional Friday or Saturday, and most holidays when I'm not travelling. In the winter half of the year with sunrise being aroung eight, I can avoid it most weekends, and stay awake all night only during holidays.
What I do? Read. Write. Writing, for me, is best done in the small hours of morning. I do not stay up after sunrise.
ETA: Well, I have. It's been a while, unless sleepless transatlantic flights count. Most recent I can remember is when I was 25, and not going into detail here. Most fun was taking the dog for an evening walk when I was 18 and returning just in time for school.</ETA>
And now I'll be very responsible and go to bed, though it's barely 1 am.